1. FIELD OF THE INVENTION
The present invention presents a method based on chemical vapor deposition reactions, particularly an enclosed-channel reactor system and a method to manufacture catalysts or support materials on the basis of atomic layer deposition (ALD).
2. DESCRIPTION OF THE PRIOR ART
Catalysts are typically applied to increase reaction rate in various processes with less energy consumption, such as fuel cells and hydrogen production by water splitting. Improving the surface area between gas phase and catalyst would be a key factor to improve the reaction rate. Therefore, to obtain well-dispersed and nanoscaled catalysts with large specific area is crucial for catalytic reactions.
The catalytic reaction can be depicted as shown in FIG. 1(a). With the help of catalyst, reactant A will be transformed to product B in a faster and energy-efficient way. In order to prevent the participation of unwanted elements, the catalytic reaction is typically contained in the enclosed-channel reactor as shown in FIG. 1(b), where the reactant A will flow through. Accordingly, the catalyst should be coated on the inner surface of channel for the catalytic reaction, as shown in FIG. 1(c). Furthermore, a thermally stable nanoscaled support, shown in FIG. 1(d), would be needed to prevent the clustering of nanoscaled catalyst, at elevated temperature, leading to reduction of surface area for catalytic reaction.
Conventionally, nanoscaled catalyst or support can be prepared by injecting liquid precursor into channels by compressed air, followed by heating at elevated temperatures. However, it is difficult to uniformly deposit the catalyst or support on channel surface with good dispersion due to restriction of channel shape or size and poor precursor liquidity. Powder metallurgy is an alternative to prepare catalyst and support by co-sintering the liquid precursor. However, only a limited amount of catalyst on the surface is available for catalytic reaction so that the utilization efficiency of catalyst is low. Therefore, it would be helpful to deposit well-dispersed nanoscaled catalyst or support on the channel surface.
Vapor deposition is considered to deposit catalyst or support material on the channel surface with a better dispersion. As shown in FIG. 2, the gaseous precursor would, however, tend to transport through peripheral path Q1 of a reactor body 12 rather than inner path Q2 due to the difference of gas conductance. The catalyst or support would tend to deposit on the surface along the outside path, which cannot serve as reaction area. Therefore, the utilization efficiency of catalyst grown by a conventional vapor deposition process would be low. Uses of extended injection duration and high concentration may lead to a thicker coating along path Q2, but the cost would increase significantly. Therefore, it is crucial to improve the coating of catalyst or support on the inner path Q2 with less consumption of precursor.